After the European Elections, Griffiths moved to Westminster to work for the Shadow Cabinet, as Chief of Staff to Theresa May, where he worked on environment, transport and later family policy. During this time, Griffiths also helped set up Women 2 Win, a campaign to get more Conservative women elected to Parliament. In 2006, Griffiths moved to work for the Culture, Media and Sport team, working as Chief of Staff to Hugo Swire MP. The next year, he focused on community cohesion and local government matters as Chief of Staff to Eric Pickles MP, Shadow Secretary of State for Communities and Local Government, and remained Pickles' Chief of Staff when he became the Party chairman. Griffiths was a member of the A-List and was selected as a candidate for Burton in November 2006.[2]

Griffiths has not joined fellow local Conservative MPs Andrew Bridgen and Heather Wheeler in campaigning for the return of passenger rail services on the Burton to Leicester railway line - the Ivanhoe Line.[4] However, he has campaigned for improvements to be made to Burton Station.[5]

In February 2015, Griffiths was awarded Parliamentarian of the Year by the Campaign for Real Ale (CAMRA) in recognition of his role in campaigning for the reduction of tax increases on beer. The award sparked controversy from some CAMRA campaigners due to Griffiths' opposition to other CAMRA campaigns on increasing planning controls on public houses, to prevent their loss, and for opposing reform to the controversial system of "beer ties" which oblige landlords to pay higher prices to the chain owners (pubcos) for their beer supplies.[8]

During Jeremy Corbyn’s response to the November 2017 Budget on 22 November 2017, Griffiths heckled him over his comments on the lack of adequate Government funding for care homes. Labour MPs accused Griffiths of ageism and abusive language for shouting that Corbyn belonged in a care home.[9] Griffiths denied this, instead suggesting that he was responding to Corbyn's statement "there are elderly people in need of help," and that he said: "That's you!"[10] Corbyn responded with the comment: "The uncaring, uncouth attitude of certain members of parliament needs to be called out".[10]

On 12 February 2018, Griffiths received extensive media coverage after he was interviewed on BBC Radio 5 Live to promote shared parental leave and said that he would not be able to take it himself when his own baby was due to be born later that year, saying, "Unfortunately, as a minister, I’m not allowed... Ministers are not allowed to take shared parental leave." The presenter, Emma Barnett, said: “Hang on a minute, back up a second, you’ve just come on the radio to promote Shared Parental Leave and you’re in a job where the rules could be changed because you are the rule-makers, where you’re not allowed to take Shared Parental Leave?” “That’s right,” responded Griffiths. “How can you say that without laughing?” asked Barnett. Griffiths said his main concern was for other parents to take advantage of the system.[11]

In March 2018, Griffiths was criticised by opposition MPs for blocking an SNP proposal for a bill that would secure the national minimum wage for those working on a "trial period" basis. It was revealed that Griffiths had previously advertised for an unpaid intern position in his own office. In response, Griffiths admitted he had used unpaid interns, but argued that the bill was not needed because existing law was already adequate in this area.[12]

On 14 July 2018, the Sunday Mirror revealed that Griffiths had resigned from his ministerial post over sexual misconduct allegations, and announced that it would publish "depraved" social media messages he had sent to female constituents the following day.[13][14] On 15 July the paper published extracts from over 2,000 text messages – many of a graphic and violent sexual nature – sent by Griffiths to two of his female constituents.[13][14] Over 5,000 people signed a petition urging him to resign as an MP and in August 2018 a demonstration took place in his constituency.

He was later suspended from the Conservative Party after allegations of inappropriate touching and bullying were made by Deneice Florence-Jukes, a serving Tory borough councillor, three months earlier.

In November 2018, during an interview with The Sunday Times, Griffiths reported that he planned to kill himself after the sexual misconduct allegations came to light. During the same interview, Griffiths claimed that the texts that he had sent to the women were "the result of my mental breakdown" following a "battle with my own mental health".[17]

On 12 December 2018, Griffiths had the Conservative whip restored, ending his suspension from the party.[18][19] His reinstation was widely criticised for being announced hours before a confidence vote in Conservative leader Theresa May, making Griffiths eligible to participate.[20]Dawn Butler said, “It is a betrayal of women for the Tories to let an MP who was suspended for sexual harassment back into their party just to allow them to vote for Theresa May in the leadership challenge.”[21]